Experimental study on the evolution of surface discharge for oil-paper insulation in transformers

Oil-paper is the main insulation of Oil-immersed power transformers. Reflecting the deterioration of insulation effectively, partial discharge (PD) has become one of the significant means to estimate the insulation condition of power transformers. Surface discharge is one of the most important type of PD. Studying the long-term process of this PD pattern, by the means of acquiring PD data and observing the length of discharge channel along the pressboard surface, this paper puts forward the descriptors and characteristics for each discharge stage, and lays the foundation for identifying the fault severity of surface discharge. In order to get reliable and objective PD data, we establish a temperature-controlled experimental platform, which can simulate the fault of surface discharge without corona under certain high voltage, and use ultra high frequency (UHF), ultra wide band (UWB), conversional Impulsive current(CIC) to study this PD evolution process. Voltage-elevating method is used to accelerate the discharge evolution, and the statistical characteristics of surface discharge process are extracted, which is from the initial discharge to the insulation breakdown. The observed data, e.g. the maximal amplitudes of PD (Urn), the number of PD (N) and the energy of PD (P), appear to have an increasing trend. The closer to breakdown, the better correspondence of the detected signals is.